This is a Continuation Application of PCT Application No. PCT/JP00/09047, filed Dec. 20, 2000, which was not published under PCT Article 21(2) in English.
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-361288, filed Dec. 20, 1999, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a digital signal transmission apparatus, particularly a digital signal transmission apparatus for use in SDH (Synchronous Digital Hierarchy) or SONET (Synchronous Optical Network). More particularly, the invention relates to an improvement of the OAM (Operation Administration and Maintenance) section incorporated in a digital signal transmission apparatus.
2. Description of the Related Art
SDH attracts attention as a digital transfer system. SDH defines an interface for effectively multiplexing various types of high-speed service and the existing low-speed service. This system is undergoing standardization at the recommendation of ITU-T.
SDH is characterized in that the basic transmission rate is 155.52 Mbps and that signals should be transmitted at an integral multiple of the basic transmission rate, i.e., 155.42xc3x97N (N is an integer) Mbps. One frame is 125 xcexcsec long, which is the basic cycle of encoding audio data, and is multiplexed in units of bytes. The frame configuration is represented by rows and columns of bytes. The frame is composed of an overhead and a payload. The overhead is arranged in the first to ninth columns. The payload is arranged in the tenth column and the remaining columns and contains main data.
The overhead consists of a section overhead (SOH), an Administrative Unit pointer (AU PTR), and a pass overhead (POH). SOH contains network management data that is used to transmit the main data. It performs various functions, such as frame synchronization, error monitoring, alarm transfer, data linking for operation administration and maintenance, system switching control, and the like. AU PTR designates the head position of the multiplexed data stored in the payload. POH has the function of transferring error alarms.
An SDN transmission apparatus comprises an OAM section for the operation administration and maintenance of the apparatus, in addition to a plurality of transmission units. The OAM section has various management/control functions, ranging from intra-apparatus management to systematic operation administration and maintenance. The intra-apparatus management includes as control of the apparatus, such as switching the apparatus now used to a reserve one, monitoring of transmission quality, failure evaluation. The systematic operation administration and maintenance includes control of transmission line installation and operation administration of the network. To perform these functions, the OAM section needs to have not only an input/output interface for the intra-apparatus modules such as transmission units, but also an input/output interface for the management data transmitted between the apparatus and an external supervisory apparatus by the use of overheads.
Generally, the OAM section of the conventional transmission apparatus has a monitor/control module equipped with a high-performance CPU. The monitor/control module carries out all functions of the OAM section. The monitor/control module of the conventional transmission apparatus therefore needs to have a large-capacity transmission port. Inevitably, the conventional transmission apparatus has a complex and gigantic structure.
Further, the monitor/control module of the conventional transmission apparatus must operate at high speeds. Its operating efficiency may decrease when the control traffic is busy due to many alarms generated. To make the matter worse, the conventional transmission apparatus has but insufficient countermeasures against troubles the monitor/control module may have.
An object of the present invention is to provide a digital signal transmission apparatus in which the control traffic concerning the operation administration and maintenance does not become busy and which can therefore be simple in structure and operate with high reliability.
To achieve the object, a digital signal transmission apparatus according to the invention has a plurality of transmission units each including a line connection unit. The transmission units transmit and receive multiplexed digital signals to and from an external transmission apparatus. The digital signal transmission apparatus comprises:
a first transmission line having a first transmission speed and a second transmission line having a second transmission speed lower than the first transmission speed;
first monitor/control units connected by the first transmission line to the plurality of transmission units, respectively, for monitoring operating condition of each transmission unit in real-time and through the first transmission line; and
a second monitor/control unit connected to the first monitor/control units by the second transmission line, for collecting monitor data concerning each transmission unit and acquired by the first monitor/control units, in real time through the second transmission line, and for monitoring the apparatus on the basis of the monitor data concerning each transmission unit and acquired by the first monitor/control units.
In the present invention, the first monitor/control units monitor the transmission units for their operating conditions, and the second monitor/control unit monitor the entire apparatus on the basis of the data representing the conditions the first monitor/control units have monitored. Thus, even the transmission units are provide in large numbers, the operation conditions of the transmission units can be monitored in real time and more reliably than in the case where a single main monitor/control module perform all controls concerning the monitoring of the transmission lines. No communication ports of large capacity need to be provided in the main monitor/control units. Nor is it necessary to perform processes at high speeds in the main monitor/control units. Thus, monitoring and control can be efficiently carried out by means of a general-purpose configuration.
The first monitor/control units are provided for the transmission units, respectively. Therefore, if any first monitor/control unit malfunctions or has a trouble, the other monitor/control units keep operating. This enhances the reliability of the apparatus.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.